Hybrid injection molding machine

ABSTRACT

An electro-mechanical drive apparatus uses a single variable speed motor, two one-way clutches, a hydraulic pump stack and a hydraulic accumulator to provide both hydraulic power for linear motion axes and rotation of a driven element of an electromechanical drive system in an injection molding machine. When engaged, the first one-way clutch couples the drive motor to the pump stack, while the second one-way clutch couples the motor to the driven element. During rotation of the drive motor in a forward direction, (a) the first one-way clutch engages, rotating the shaft of the hydraulic pump stack to power the machine&#39;s hydraulic systems and charge an accumulator; and (b) the second one-way clutch slips. When the drive motor is rotated in a reverse direction, (a) the second one-way clutch engages, rotating the driven element, and (b) the first one-way clutch slips.

This is a continuation-in-part of application Ser. No. 08/901,752, filedJul. 28, 1997, now U.S. Pat. No. 5,916,602.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to injection molding machinesand, more particularly, to an injection molding machine that uses asingle electric motor to rotate a driven element of an electromechanicalsystem and, alternatively, drive a hydraulic pump stack.

2. Description of the Related Art

The injection unit of a typical injection molding machine providesessentially two functions during the course of a normal cycle ofoperation; namely, injection and extruder. The injection function occurswhen the feed screw is moved forward linearly (without rotation) toforce plastic melt into the mold. The extruder function is accomplishedwhen the feed screw is rotated to plasticize additional material for thenext shot. As the feed screw is rotated during the extruder function,the plastic melt is gradually forced past the end of the screw, creatinga pressure or force to move the screw rearward to its pre-injectionposition as the melt accumulates.

Both the injection and extruder functions require an associated driveapparatus in the injection unit. In prior art hydraulic machines, themovement for the injection function is typically performed by ahydraulic cylinder, while the rotation of the feed screw for extruderrun is normally accomplished by a hydraulic motor. More recently,electric motors combined with mechanical systems have been used as thedirect power source in the injection unit. Some of the prior artelectric systems have used separate motors for each function; i.e., onemotor for rotating the feed screw and a second motor in combination witha mechanism, such as a ball screw, to convert rotary motion into thelinear movement required for injection. Other prior art "hybrid"machines have used an electric motor to rotate the feed screw with theremaining functions of the machine being hydraulically driven, withpower provided by another electric motor diving one or more hydraulicpumps.

While the prior art "hybrid" machine incorporates some of the advantagesof both electric (better, more efficient, control of screw rotation) andhydraulic (lower overall cost) machines, there remains room forimprovement. In particular, there is potential for a more economicalsystem since there is excess capacity in the electric motor that rotatesthe screw. This motor is only used during the portion of the cycle werethe thermoplastic material is extruded (plasticated) to build the shot.Typically this is around 50% or less of total cycle time. In addition,the extruder function requires steady power, in contrast to other motionaxes on the typical injection molding machine which require short burstsof high power relative to the total power averaged over the total cycletime. Therefore the motor for the extruder axis is a logical choice(although not the only choice for every application) to be the driverfor a hydraulic power source, possibly including a hydraulicaccumulator, used for other axes requiring intermittent high power tooperate. Since the motor and the associated variable speed drive have arelatively high cost, it is desirable to maximize the utilization ofthis motor. Furthermore, for the injection molding machines withvariable speed motors currently available, the motors are eitherdedicated to specific axes (as with electromechanical systems), or areapplied to standard hydraulic circuits redundantly so that no economy ofcontrol is gained by the variable speed motor and drive.

Finally, one of the limitations in full-electric machines is the maximuminjection rate (acceleration) attainable with current mechanisms drivenby an electric motor. It would be desirable to use the "hybrid" machineconcept to take advantage of the injection speed of an accumulatorhydraulic system combined with the advantages of an otherwise electricmachine.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a driveapparatus that is simple in construction and effectively enables asingle variable speed motor to be used to provide power for acombination of mechanical and hydraulic machine elements.

Briefly stated, in the preferred embodiment, the present invention isdirected to a drive apparatus including a variable speed motor, such asbrushless DC, AC Vector, or AC servo, and conventional powertransmission components to alternately provide (a) rotation of the feedscrew in the injection unit of an injection molding machine or (b)operation of a hydraulic pump stack in order to provide power to themachine's hydraulic system. The drive apparatus further includes a firstone-way clutch between the motor and the feed screw, and a secondone-way clutch between the motor and the hydraulic pump stack.

During operation of the most machine functions, the drive motor isrotated in a forward (clockwise) direction to rotate the input shaft ofthe pump stack, thereby providing hydraulic power for the operatingelements in the various motion axes. For a primarily hydraulic machinethis would likely include all primary linear axes, such as clamp,injection and eject. For an otherwise electric machine, the hydraulicsmight be limited to only one or two axes, such as injection and/oreject. Specifically, during forward rotation of the drive motor, (a) thefirst one-way clutch is engaged, rotating the shaft of the pump stack;and (b) the second one-way clutch slips.

It is important to note that the hydraulic power from the pump stack canalso be used to charge a hydraulic accumulator, providing a hydraulicpower reserve for intervals when the motor is not available to drive thepump. This makes the present invention uniquely superior to otherhydraulic hybrid machines. Since servomotors are used to charge thehydraulic accumulator, power is consumed in equivalence to the hydraulicenergy required by the process to perform the desired motion on themachine. Once the accumulator is charged the motor shuts-off completely.

The motor is rotated in a reverse (counterclockwise) direction toaccomplish the extruder function, i.e., to rotate the feed screw througha suitable transmission mechanism. In particular, during reverserotation, (a) the second one-way clutch is engaged, rotating the feedscrew via pulleys and a drive belt at a predetermined speed toplasticize material; and (b) the first one-way clutch slips.

The simplest embodiment of the drive apparatus includes a double shaftmotor mounted to engage suitable power drive couplings for the feedscrew and the hydraulic pump stack. However, a single shafted motor isequally applicable with the clutch being mounted between the drivenpulley and the driven device, (pump stack, extruder screw, linearactuator, etc). Overall, the present invention provides a compact drivesystem for a single motor to power all machine axes; this improvesreliability and allows faster response over prior art systems thatrequire a shift mechanism to divert power to the different axes.Advantages of the preferred embodiment include: better utilization ofmotor capacity, improved energy efficiency, reduced overall machine costand more accurate control of feed screw rotation.

Certain families of applications for injection molding can be moreefficiently practiced using variations of the present invention. Forexample, injection molding of thin-wall packaging requires thecapability of operating at very high injection rates for very shorttimes. As noted previously, one of the limitations in full-electricmachines is the maximum injection rate (acceleration) attainable withcurrent mechanisms driven by an electric motor. With the drivearrangement of the present invention, it is possible to take advantageof the injection speed of an accumulator hydraulic system combined withthe advantages of an otherwise electric machine.

Another example involves manufacture of plastic pipe fittings. Here theplasticizing cycle is very long because of large shot weights and hightorques required by materials to be processed. Cycle times are very longbecause of heavy wall thicknesses requiring long cooling cycles. As aresult duty cycles on clamp and eject axes are extremely low becausethey only operate for such a small portion of the total cycle. Here,full electrification of these axes is not as cost effective aselectrification of these same axes for applications that might use thesame functioning much more frequently, possibly five to ten times asoften. For making plastic pipe fittings and other parts with similarshot size and cycle time relationships, a hybrid machine according tothe present invention with dual electrically driven functionality on theextruder axis for plastication and hydraulic power generation isarguably the most efficient alternative.

Those skilled in the art will be able to cite other specific examples ofapplications in which an imbalance occurs on various functional axes ofthe machine in such a way as to make it economical to applyhybridization as described above. Any axis can be driven electricallyand if the duty cycles of other axes are sufficiently low, the reservecapacity of any axis can be used to generate power to drive the lowerduty cycle axis or axes as long as the power drive axis only requires asingle rotational direction to carry out its primary function.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of an injection molding machine,including a drive apparatus according to the present invention.

FIG. 2 is a right end elevational view of the injection molding machineillustrated in FIG. 1.

FIG. 3 is a top plan view of the injection molding machine illustratedin FIG. 1.

FIG. 4 is an enlarged, fragmentary side elevational view, partially insection, taken along the line 4--4 in FIG. 3.

FIG. 5 is an enlarged, fragmentary view, partially in section, of thedrive apparatus shown in FIG. 4, with certain parts removed for clarity.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be described in connection with a typicalhydraulic injection molding machine 1 that includes a clamping system 2and an injection unit 10 with an electric screw drive. It should benoted, however, that the advantages of the invention can be applied toinjection molding machines having multiple axes drivenelectro-mechanically, as are known in the art. As shown in FIG. 1 and 4,the injection unit 10 is carried by horizontal support rods 4 attachedto a base 8 of the injection molding machine 1. The injection unit 10 isadapted to move along the support rods 4 for purposes of positioning,such as making connection with a mold (not shown) attached to stationaryplaten 6.

The primary components of the injection unit 10 include a barrel 12containing a feed screw 14 (FIG. 4) that works to plasticizethermoplastic material that enters the barrel 12 through housing 15 fromhopper 16. The operative functions of the injection molding machine 1,including the injection unit 10, are initiated by a drive assembly 18.The drive assembly 18 of injection unit 10 includes an electric drivemotor 20, pump drive coupling 22, extruder drive coupling 24, hydraulicpump stack 26 and support housing 28, see FIGS. 2 and 4. As will bedescribed in greater detail in the following paragraphs, the driveassembly 18 operates to rotate the feed screw 14 to plasticize thematerial during the extruder function, and to generate the hydraulicpower required for the other machine functions.

Referring more particularly to FIG. 5, the drive assembly 18 includes apump drive coupling 22 that connects the motor 20 to the hydraulic pumpstack 26. Mounted on the shaft 38 of motor 20 are a one-way clutch 42and two ball bearing assemblies 44, which collectively serve to supportand engage a connector sleeve 40 that attaches directly to the shaft 34of the pump stack 26. As will be more fully described later, while themotor 20 is capable of rotation in either direction, the one-way clutch42 acts to allow rotation of the pulley 40 in one direction only. In thecontext of this disclosure, each element described as a "one-way clutch"is preferably a mechanical cam type clutch made to engage a rotatingcylindrical element with a surrounding member for one direction ofrotation; there is essentially no resistance from the clutch when theelement is rotated in the opposite direction. Morse Industrial, EmersonPower Transmission Corp., is a well known supplier of this type ofclutch.

A motor mounting plate 51 connects directly to a support housing 36 andis configured to travel with the support housing 28 along the guide rods30. As shown, the motor 20 sits directly on top of the mounting plate51.

The drive assembly 18 also includes an extruder drive coupling 24 toconnect the motor 20 to the feed screw 14. In a manner similar to thatdescribed above for the pump drive coupling 22, the extruder drivecoupling 24 includes a pulley 64 mounted on motor shaft 38 through aone-way clutch 66 and bearings 68. A second pulley 72 in extruder drivecoupling 24 connects to the feed screw 14 and is driven by pulley 64through a drive belt 70.

Although the drive assembly is shown with a double shaft motor, thoseskilled in the art will appreciate that double shafted constructions arenot widely available for large size servomotors. Accordingly, singleshafted motor can also be used in the drive assembly of the presentinvention with the necessary clutches interposed between the drivenpulley and the driven devices, (pump stack, extruder screw, linearactuator, etc). More specifically, the driving pulley is mechanicallyconnected to the electric motor shaft, and connected to the two otherdriven pulleys/clutches with a single belt or separate belts, asrequired. Other suitable drive configurations can be contrived,depending on machine construction and the relative orientation of thedriven devices.

The operation of the drive assembly 18 will now be described. Toinitiate the extruder function, motor 20 is activated to rotate in acounterclockwise direction. This rotation of motor shaft 38 causesone-way clutch 66 to engage, driving pulley 64 and, consequently, pulley72 by virtue of drive belt 70. The rotation of pulley 72 imparts likerotation to the feed screw 14. As the feed screw 14 is rotated, materialsupplied from hopper 16 feeds through housing 15 and is plasticizedwithin barrel 12. The rotation of feed screw 14 also serves to advancematerial toward the nozzle (discharge) end of barrel 12, causing thepressure of the melt to increase at the end of the screw 14 as thecharge of material begins to accumulate. When the pressure of theplastic melt reaches a certain level, it will begin to force feed screw14 rearward, thereby moving the entire drive assembly 18 to the rear ofinjection unit 10. Specifically, the rearward movement of feed screw 14applies a force to housing 36, causing housing 36 to move likewise tothe rear, carrying motor 20, pump stack 26 and associated drivecomponents.

The rate of rearward movement of the feed screw 14 can be controlled bythe hydraulic cylinders 46 connected to either side of the housing 36(see FIG. 1). The appropriate valving of the fluid in the cylinders 46can slow the rearward movement (but not the rotation) of the feed screw14, thereby increasing the back pressure of the plastic melt.Alternatively, the hydraulic cylinders 46 can be used to apply force onthe housing 36 in a way that increases the rate at which the feed screwmoves back, thereby decreasing the back pressure of the melt.

As the motor 20 rotates in a counterclockwise direction during theextruder function, the one-way clutch 42 slips on shaft 38 so that norotational force is transmitted to the pump shaft 34. The extrusionfunction is complete when a sufficient charge of plastic melt isaccumulated in front of the feed screw 14, as required to fill thecavity of the mold mounted on the stationary platen 6.

As soon as the extrusion function is complete, the motor 20 is reversedso that it rotates in a clockwise direction; as a result, one-way clutch42 is engaged on shaft 38, rotating connector sleeve 40 and shaft 34 ofthe hydraulic pump stack 26. The hydraulic energy generated by the pumpstack 26 is used to operate associated machine functions and/or charge ahydraulic accumulator 48, as determined by the operating sequence andparticular construction of the injection molding machine 1. For example,in machines where the injection function is performed by a hydraulicsystem, hydraulic energy is directed via suitable valving (not shown) tothe hydraulic cylinders 46; the cylinders operate to impart atranslational (linear) movement to the feed screw 14 by applying a forceto the housing 36. Note that for systems including an accumulator 48,the motor 20 is deactivated after the desired hydraulic pressure chargeis achieved.

The forward movement of feed screw 14 causes the plastic meltaccumulated at the end of the barrel to be forced out of the barrel andinto the mold cavity. During injection, a braking motor 50 is energizedto impart sufficient force to the drive belt 70 to keep the feed screw14 from rotating in a clockwise direction when the feed screw 14 ismoved forward to inject the plastic melt. (The force of the plastic melton the flight of the feed screw 14 creates a torque that tends to rotatefeed screw 14.) Upon completion of the injection function, the cylinders46 are used to maintain pressure on the plastic melt ("pack and hold) toensure that the part is properly formed.

At the beginning of the pack and hold interval, the motor 20 reversesrotation to begin another extrusion function, as described previously.The accumulator 48 provides the hydraulic energy required to maintainoperation of the cylinders 46 while the motor 20 is rotating the feedscrew. Similarly, the accumulator 48 would provide the hydraulic energyto open the mold after pack and hold is complete. Depending on theduration of the extrusion operation, the hydraulic energy required tooperate other axes, such as part ejection and/or closing the clampsystem in preparation for injection, is supplied by the accumulator 48and/or pump stack 26, as required by the components of the injectionmolding machine 1.

While the invention has been illustrated in some detail according to thepreferred embodiment shown in the accompanying drawings, and while thepreferred embodiment has been described in some detail, there is nointention to thus limit the invention to such detail. On contrary, it isintended to cover all modifications, alterations, and equivalentsfalling within the spirit and scope of the appended claims. For example,although the drive couplings are generally described as belts andpulleys, other mechanical couplings, such as suitable gearing, can beused to perform the same function. In addition, although the inventionis shown in conjunction with a machine that is primarily hydraulic, itcan also be incorporated in machines that primarily comprise systemsthat are electro-mechanically driven.

What is claimed is:
 1. An injection molding machine comprising at leastone hydraulically operated system, an injection unit including a feedscrew capable of rotational and translational movement within a barrel,a hydraulic pump, a variable speed electric drive motor, andtransmission means for alternately transmitting power from the drivemotor to (a) rotate the feed screw and (b) activate the hydraulic pump,such that operation of the drive motor in one direction rotates the feedscrew to plasticize material in the barrel of the injection unit andoperation of the drive motor in an opposite direction activates thehydraulic pump to enable operation of the hydraulic systems of theinjection molding machine.
 2. The injection molding machine of claim 1wherein the transmission means comprises:(a) a first one-way clutchinterposed between the drive motor and the hydraulic pump, and (b) asecond one-way clutch interposed between the drive motor and the feedscrew, such that when the drive motor is operated in a forwarddirection,(i) the first one-way clutch is engaged to operate thehydraulic pump thereby generating hydraulic power to operate thehydraulic systems of the injection molding machine, and (ii) the secondone-way clutch slips; when the drive motor is operated in a reversedirection,(iii) the second one-way clutch is engaged, rotating the feedscrew, and (iv) the first one-way clutch slips.
 3. A molding machinehaving at least one hydraulically operated system, an injection unitincluding a feed screw rotatably and translatably carried in a barrel, ahydraulic pump, a variable speed electric drive motor, and transmissionmeans for alternately transmitting power from the drive motor to thefeed screw and hydraulic pump, the transmission means comprising:(a) afirst one-way clutch interposed between the drive motor and thehydraulic pump, (c) a second one-way clutch interposed between the drivemotor and the feed screw, such that when the drive motor is operated ina forward (pump) direction,(i) the first one-way clutch is engaged tooperate the hydraulic pump thereby generating power to operate thehydraulically operated systems, and (ii) the second one-way clutchslips; when the drive motor is operated in a reverse (extrusion)direction,(iii) the second one-way clutch is engaged, rotating the feedscrew, and (iv) the first one-way clutch slips.
 4. An injection moldingmachine comprising at least one hydraulically operated system, at leastone electro-mechanical drive system including a variable speed electricdrive motor, a hydraulic pump, and transmission means for alternatelytransmitting power from the drive motor to (a) rotate a driven elementin the electro-mechanical drive system and (b) activate the hydraulicpump, such that operation of the drive motor in one direction activatesthe electromechanical drive system and operation of the drive motor inan opposite direction activates the hydraulic pump to enable operationof the hydraulic systems of the injection molding machine.
 5. Theinjection molding machine of claim 4 wherein the transmission meanscomprises:(a) a first one-way clutch interposed between the drive motorand the hydraulic pump, and (b) a second one-way clutch interposedbetween the drive motor and the driven element, such that when the drivemotor is operated in a forward direction,(i) the first one-way clutch isengaged to operate the hydraulic pump thereby generating hydraulic powerto operate the hydraulic systems of the injection molding machine, and(ii) the second one-way clutch slips; when the drive motor is operatedin a reverse direction,(iii) the second one-way clutch is engaged,rotating the driven element, and (iv) the first one-way clutch slips.